One of the things noticed using the 5D2 during the Great Zacuto Shootouts is that the in between ISO settings render cleaner images. I don't remember the particulars, but and of the multiples on the 5D2, 160, 320, 640, 1280, perhaps higher, gave cleaner vid than the normal ISO progression.

I don't recall if this was for all or just the 5D2. Worth checking their website for the comparison and then testing on your own.

I believe the explanation centers around the difference between shot noise and read noise. While one can be better at 640 than 400 (not sure about 100 though), the other type of noise more than compensates, thus the end result has more total noise. If I am not mistaken, the lens-cap-on test measures just one type of noise.

You never want to PUSH the ISO. And be warned that PULLING the ISO will reduce the dynamic range by 1/3 stop. It is always better to pull than to push. And pulling is better than NATIVE when shooting low dynamic range scenes at high ISOs.

Andrew: Can we assume you used flash as the lighting source in order to keep the exposure settings constant even though there is a 3 stop difference in ISO settings or did you change your raw processing settings?

Andrew: Can we assume you used flash as the lighting source in order to keep the exposure settings constant even though there is a 3 stop difference in ISO settings or did you change your raw processing settings?

Nope, no flash. Everything set on manual. Just alter the ISO setting with original aperture and shutter the same.

If increasing ISO did not improve noise, in a light-starved situation, it would be a worthless feature. You have successfully demonstrated that the ISO setting does exactly what it is supposed to do. Of course if you had provided 8x as much light to the ISO 100 test, that image would then be the one with lower noise.

If increasing ISO did not improve noise, in a light-starved situation, it would be a worthless feature.

True although in this example it wasn’t a light starved situation. The same shutter and aperture was used for both captures.

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You have successfully demonstrated that the ISO setting does exactly what it is supposed to do. Of course if you had provided 8x as much light to the ISO 100 test, that image would then be the one with lower noise.

I only adjusted the ISO setting. But yes, had the 100 ISO image had those two stops more photons and had been equality normalized, it would look better than the ISO 800 image.

I only adjusted the ISO setting. But yes, had the 100 ISO image had those two stops more photons and had been equality normalized, it would look better than the ISO 800 image.

So let me get this straight. What does the in-camera histogram look like for your two shots? If the ISO 100 shot was exposed to the left and the ISO 800 was ETTR, then I can understand why the ISO 100 is noiser. The arguement I raised and the sources I referenced assume that each compared shot is normalized in camera, not in Photoshop (ie, exposed in the middle of the histogram in camera). If you compare apples to apples, ISO 100 will always have less noise than ISO 800.

So let me get this straight. What does the in-camera histogram look like for your two shots?

I have no idea. Didn’t look, don’t care. I’m capturing raw data, the in-camera histogram is immaterial in this case.

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If the ISO 100 shot was exposed to the left and the ISO 800 was ETTR, then I can understand why the ISO 100 is noiser.

Yes, exactly! You got it. The ISO 100 was exposed to the left but based on what the incident meter (which hasn’t a clue about raw or ETTR) recommended.

But the important point here is the concept which some believe, that in all cases, an image captured at ISO 100 will always have a lower level of noise than one shot at ISO 800. That isn’t necessarily the case.

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If you compare apples to apples, ISO 100 will always have less noise than ISO 800.

But the important point here is the concept which some believe, that in all cases, an image captured at ISO 100 will always have a lower level of noise than one shot at ISO 800. That isn’t necessarily the case.

This must be a misunderstanding. Anyone who believes that ISO 100 is always less noisy than ISO 800, would have to believe that camera makers are maliciously supplying an adjustment knob which you can use to make your pictures worse. The real situation is quite simple: when you have enough light to expose properly, ISO 100 will require 8x (three stops) more light than ISO 800 and will be less noisy. Conversely, when you do not have enough light, setting ISO 800 will reduce noise, compared to simply underexposing ISO 100. This is precisely the case in which you would use ISO 800, as a tool to reduce noise.